This invention relates to a method of producing sucrose fatty acid ester (hereinafter sometimes referred to as "SE") granules by the fluidized bed granulation and drying technique.
Sucrose fatty acid esters (hereinafter sometimes referred to as "SEs") can be widely variegated in HLB value (hydrophile-lipophile balance value) and are used as nonionic surfactants in various fields. In particular, it is a recent trend to use them by preference as tasteless, odorless, nontoxic food additives.
Meanwhile, sucrose fatty acid esters currently on the market are mostly in the form of powders and, in some instances, in the form of aqueous solutions or lumps. No granulated SEs have been known as yet.
Such SE powders have a particle size distribution such that 90% or more can pass a 150-mesh sieve. Thus they contain a fine powder fraction in considerably large amounts. These SE powders are disadvantageous in:
(1) That, in handling them, the fine powder fraction rises as a cloud of dust;
(2) That, in the case of highly hydrophilic SEs, time is required for the dissolution thereof in water, since, on that occasion, SE particles stick together to form undissolved lumps; and
(3) That said SE powders are poor in flowability.
Therefore, granular SEs which are easy to handle are desired. To date, a few proposals have been put forward for a method of granulating SEs or a method suggestive thereof.
Thus, for instance, Japanese Patent Publication No. 45-3524 proposes a method of producing granules which comprises allowing a powder to be granulated to fall spontaneously within a granulation column and come into contact with a gentle countercurrent of heated ordinary-pressure steam. However, when applied to a powdery SE, this method may allow the SE, which is a mixture of esters differing in the degree of esterification and has a wide melting range, to melt at temperatures not lower than 50.degree. C. Conversely, at temperatures lower than 50.degree. C., it is difficult to evaporate the moisture in the mass of particles moistened as a result of the use of steam at the granulation column height proposed, hence the powder is apt to cake.
Japanese Laid-Open Patent Publication KOKAI No. 54-32176 discloses a method of granulation and drying by the fluidized bed technique which comprises spraying a powder forming a fluidized bed with a binding agent. However, when water alone is used as the binding agent in carrying out this method for the granulation and drying of an SE, SE particles can grow to great granules but the granules are fragile and readily disintegrate upon collision with one another during drying. Although said method includes the use, as the binding agent, of a water-soluble macromolecular substance having great binding ability, such as CMC or PVA, the use of such binding agent decreases the purity of the SE, hence poses a restricted-use problem. Thus, the SE granules produced by this method cannot be regarded as food additive grade SEs as specified in the Japanese Food Additives Standards but can be used only as food additive compounds.
A granulation method disclosed in Japanese Patent Publication No. 53-1249 comprises adding a binding agent to an SE, kneading the mixture and then crushing the kneaded mixture. In this method, the frictional heat due to stirring in the steps of kneading and crushing readily causes a temperature rise, which results in melting or remelting of the SE. As a result, it is difficult to obtain granulation products desirable in size. Furthermore, when alcohol is used additionally as a binding agent, the working environment is contaminated and at the same time safety problems arise, for instance the alcohol vapor may catch fire.
Furthermore, the fact that no granulated SE products have been marketed until today is nothing but an implication that the granulation methods so far reported or proposed have problems in the practice thereof.